Structural concrete, though capable of carrying very high compressive loads, is generally weak in carrying tensile loads on its own. Reinforced concrete ameliorates this deficiency by including an internal structure formed from materials capable of withstanding tensile forces within an otherwise solid concrete structure. Metal bars or cables are often used due to their high tensile strength and relative ease of manufacture.
In order to further improve the tensile capacities of reinforced concrete structures, the reinforcement structure may be pre- or post-tensioned. Added structural tension maintains a compression loading on the concrete member, even when tensile stress would otherwise occur (such as in beam-loading). In post-tensioned concrete, the reinforcing structure is tensioned after the concrete has set.